Surgery performed on some part of the NERVOUS SYSTEM, whether brain, spinal cord or nerves. Disorders treated by neurosurgeons include damage to the brain, spinal cord and nerves as a result of injury; tumours in the CENTRAL NERVOUS SYSTEM; abnormalities of blood vessels in or supplying blood to the brain – for example, ANEURYSM; brain abscess; bleeding inside the skull; and certain birth defects such as HYDROCEPHALUS and SPINA BIFIDA.